n the previous chapter, you have

learnt how animals reproduce. It is

only after ‘growing up’ to a certain

age that human beings and many other

animals can reproduce. Why can

humans reproduce only after a certain

age?

In this chapter, you will learn about

changes that take place in the human

body after which a person becomes

capable of reproduction.

In Chapter

you

have learnt about

human reproductive organs. Here, we

shall discuss the role that hormones play

in bringing about changes that make a

child grow into an adult.

7.1 Adolescence and Puberty

Boojho was celebrating his 12th

birthday. After his friends left, Boojho

and Paheli began chatting with their

parents. Paheli studies in an all-girls

school. She started laughing. She

remarked that many of Boojho’s school

friends, whom she met after a year, had

suddenly shot up in height. Some of

them were looking very funny with a

hairy line above their lips. Her mother

explained that the boys had grown up.

Growth begins from the day one is

born. But upon crossing the age of 10

or 11, there is a sudden spurt in growth

which becomes noticeable. The changes

taking place in the body are part of

growing up. They indicate that you are

I wonder how long this

period marked by changes

in the body will last!

no longer a child but are on the way to

becoming an adult.

It is a strange period of life

when you are neither a child nor

an adult. I wonder whether this

period between childhood and

adulthood had a special name!

Growing up is a natural process. The

period of life, when the body undergoes

changes, leading to reproductive

maturity, is called adolescence.

Adolescence begins around the age of

11 and lasts upto 18 or 19 years of age.

Since this period covers the ‘teens’ (13

to 18 or 19 years of age), adolescents

are also called ‘teenagers’. In girls,

adolescence may begin a year or two

earlier than in boys. Also, the period of

adolescence varies from person to person.

The human body undergoes several

changes during adolescence. These

changes mark the onset of puberty. The

most important change which marks

puberty is that boys and girls become

capable of reproduction. Puberty ends

when an adolescent reaches reproductive

maturity.

EACHING

THE

DOLESCENCE

EACHING

THE

DOLESCENCE

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% of full height

Boys Girls

8 72%

77%

9 75%

81%

10 78% 84%

11 81% 88%

12 84% 91%

13 88% 95%

14 92% 98%

15 95% 99%

16 98% 99.5%

17 99% 100%

18 100% 100%

Age in

Years

Paheli and Boojho

realised that sudden

increase in height and

hairy line above the lips

in boys were signs of

adolescence. They

wanted to know more

about other changes at

puberty.

7.2 Changes at Puberty

Increase in Height

The most conspicuous change during

puberty is the sudden increase in

height. At this time the long bones, that

is, the bones of the arms and the legs

elongate and make a person tall.

Activity 7.1

The following chart gives the

average rate of growth in height of

boys and girls with age. The figures

in columns 2 and 3, give the

percentage of the height a person

has reached at the age given in

column 1. For example, by the age

11, a boy has reached 81% of his

probable full height, while a girl

has reached 88% of her full

height. These figures are only

representative and there may be

individual variations.

Use the Table for your friends

and work out how tall they are likely

to be. Find out who is likely to be

Calculation for full height (cm)

( )

100

Present height cm

% of full height at this age

(as given in the chart)

Example:

A boy is 9 years old and 120 cm

tall. At the end of the growth period

he is likely to be

120

100

cm = 160 cm tall

the tallest and who might be the

shortest in your class.

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REACHING THE AGE OF ADOLESCENCE

There is no need for Paheli to worry.

All parts of the body do not grow at the

same rate. Sometimes the arms and legs

or hands and feet of adolescents look

oversized and out of proportion with the

body. But soon the other parts catch

up and result in a proportionate body.

You must have noticed that height

of an individual is more or less similar

to that of some family member. This is

because height depends on the genes

inherited from parents. It is, however,

very important to eat the right kind of

food during these growing years. This

helps the bones, muscles and other

parts of the body get adequate

nourishment for growth. You will find

nutritional needs of adolescents

discussed later in the lesson.

Change in Body Shape

Have you noticed that boys in your class

have broader shoulders and wider chests

than boys in junior classes? This is

because they have entered the age of

puberty when shoulders generally

broaden as a result of growth. In girls,

the region below the waist becomes

wider.

In boys, the muscles of the body grow

more prominently than in the girls.

Thus, changes occurring in adolescent

boys and girls are different.

Voice Change

Did you notice that sometimes the voice

of some of the boys in your class cracks?

At puberty, the voice box or the larynx

begins to grow. Boys develop larger voice

boxes. The growing voice box in boys can

be seen as a protruding part of the throat

Activity 7.2

Use the data given in Activity 7.1 to

draw a graph. Take age on the

X-axis and per cent growth in height

on the Y-axis. Highlight the point

representing your age on the graph.

Find out the percentage of height

you have already reached. Calculate

the height you might eventually

reach. Tally your graph with the one

given here (Fig. 7.1).

Fig. 7.1 : Graph showing percentage of height

with age

I am worried. Though I

have become taller, my

face looks much smaller

compared to my body.

Initially, girls grow faster than boys

but by about 18 years of age, both reach

their maximum height. The rate of

growth in height varies in different

individuals. Some may grow suddenly

at puberty and then slow down, while

others may grow gradually.

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and pimples on the face at this time

because of the increased activity of these

glands in the skin.

Development of Sex Organs

Look up Fig. 6.1 and 6.3 of the

previous lesson which show sex

organs of humans. At puberty, male

sex organs like the testes and penis

develop completely. The testes also

begin to produce sperms. In girls, the

ovaries enlarge and eggs begin to

mature. Also ovaries start releasing

mature eggs.

Reaching Mental, Intellectual and

Emotional Maturity

Adolescence is also a period of change

in a person’s way of thinking.

Adolescents are more independent than

before and are also self conscious.

Intellectual development takes place and

they tend to spend considerable time

thinking. In fact, it is often the time in

one’s life when the brain has the

greatest capacity for learning.

Sometimes, however, an adolescent may

feel insecure while trying to adjust to

the changes in the body and mind. But

as adolescent learners, you should know

that there is no reason to feel insecure.

These changes are a natural part of

growing up.

7.3 Secondary Sexual

Characters

You have learnt in Chapter 6, that

testes and ovaries are the reproductive

organs. They produce the gametes,

that is, sperms and ova. In girls,

breasts begin to develop at puberty

Many of my classmates

have a hoarse voice. Now I

know why?

Fig. 7.2 : Adam’s apple in a grown up boy

called Adam’s apple (Fig. 7.2). In girls,

the larynx is hardly visible from the

outside because of its small size.

Generally, girls have a high pitched voice,

whereas boys have a deep voice. In

adolescent boys, sometimes, the muscles

of the growing voice box go out of control

and the voice becomes hoarse. This state

may remain for a few days or weeks after

which the voice becomes normal.

A few glands such as sweat glands,

oil glands and salivary glands release

their secretions through ducts.

Endocrine glands release hormones

directly into the bloodstream. So, they

are also termed ductless glands.

Increased Activity of Sweat and

Sebaceous Glands

During puberty the secretion of sweat

glands and sebaceous glands (oil glands)

increases. Many young people get acne

Adam’s

apple

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REACHING THE AGE OF ADOLESCENCE

and boys begin to grow facial hair, that

is, moustaches and beard. As these

features help to distinguish the male

from the female they are called

secondary sexual characters. Boys

also develop hair on their chest. In

both, boys and girls, hair grows under

the arms and in the region above the

thighs or the pubic region.

Paheli and Boojho have now

understood that puberty marks the

beginning of the reproductive period

when one becomes capable of

reproduction. But they want to know

if reproductive life, once begun,

continues, or it ends some time.

The testes and ovaries secrete sex

hormones. You have just learnt that

these hormones are responsible for the

male and female secondary sexual

characters. Further, the sex hormones

are under the control of hormones from

the pituitary gland (Fig. 7.3). The

pituitary secretes many hormones, one

of which makes ova mature in the

ovaries and sperms form in the testes.

Both Boojho and Paheli wish to know

what initiates changes at puberty.

Fig. 7.3 : The onset of puberty is controlled by

hormones

The changes which occur at

adolescence are controlled by

hormones. Hormones are chemical

substances. These are secretions from

endocrine glands, or endocrine system.

The male hormone or testosterone

begins to be released by the testes at

the onset of puberty. This causes

changes in boys about which you have

just learnt, for example, the growth of

facial hair. Once puberty is reached in

girls, ovaries begin to produce the female

hormone

or estrogen which makes the

breasts develop. Milk secreting glands

or mammary glands develop inside the

breasts. The production of these

hormones is under the control of

another hormone secreted from an

endocrine gland called pituitary gland.

7.4 Role of Hormones in

Initiating Reproductive

Function

Endocrine glands release hormones

into the bloodstream to reach a

particular body part called target site.

The target site responds to the

hormone. There are many endocrine

glands or ductless glands in the body.

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7.5 Reproductive Phase of

Life in Humans

Adolescents become capable of

reproduction when their testes and

ovaries begin to produce gametes. The

capacity for maturation and production

of gametes lasts for a much longer time

in males than in females.

In females, the reproductive phase of

life begins at puberty (10 to 12 years of

age) and generally lasts till the age of

approximately 45 to 50 years. The ova

begin to mature with the onset of

puberty. One ovum matures and is

released by one of the ovaries once in

about 28 to 30 days. During this

period, the wall of the uterus becomes

thick so as to receive the egg, in case

it is fertilised and begins to develop.

This results in pregnancy. If

fertilisation does not occur, the

released egg, and the thickened lining

of the uterus along with its blood

vessels are shed off. This causes

bleeding in women which is called

menstruation. Menstruation occurs

once in about 28 to 30 days. The first

menstrual flow begins at puberty and

is termed menarche. At 45 to 50 years

of age, the menstrual cycle stops.

Stoppage of menstruation is termed

menopause. Initially, menstrual cycle

may be irregular. It take some time to

become regular.

Menstrual cycle is controlled by

hormones. The cycle includes the

maturation of the egg, its release,

thickening of uterine wall and its

breakdown if pregnancy does not

occur. In case the egg is fertilised it

begins to divide and then gets

embedded in the uterus for further

development as you have learnt in

Chapter 6 (Fig. 6.8).

7.6 How is the Sex of the

Baby Determined?

I heard my mother and my

aunt talking about my cousin

who is going to have a baby.

They were discussing whether

she would give birth to a boy

or a girl. I wonder what makes

the fertilised egg develop

either into a boy or a girl!

Paheli says that the

reproductive life of a

woman lasts from

menarche to menopause.

Is she right?

Boy or Girl?

Inside the fertilised egg or zygote is the

instruction for determining the sex of

the baby. This instruction is present in

the thread-like structures, called

chromosomes in the fertilised egg.

Chromosomes are present inside the

nucleus of every cell. All human beings

have 23 pairs of chromosomes in the

nuclei of their cells. Two chromosomes

out of these are the sex chromosomes,

named X and Y. A female has two X

chromosomes, while a male has one X

and one Y chromosome. The gametes

(egg and sperm) have only one set of

chromosomes. The unfertilised egg

always has one X chromosome. But

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REACHING THE AGE OF ADOLESCENCE

sperms are of two kinds. One kind has

an X chromosome, and the other kind

has a Y chromosome.

See Fig. 7.4. When a sperm

containing X chromosome fertilises the

egg, the zygote would have two X

chromosomes and develop into a female

child. If the sperm contributes a Y

chromosome to the egg (ovum) at

fertilisation, the zygote would develop

into a male child.

and ovaries to produce their hormones.

You have already learnt that the

pituitary gland is an endocrine gland.

It is attached to the brain.

Apart from the pituitary, the testes

and the ovaries, there are other

endocrine glands in the body such as

thyroid, pancreas and adrenals

(Fig. 7.5).

Fig. 7.4 : Sex determination in humans

boy

girl

sperms

eggs

Now you know that the sex

chromosomes of the father determine the

sex of an unborn baby. The belief that

the mother is responsible for the sex of

her baby is completely wrong and to

blame her for this is totally unjustified.

7.7 Hormones other than

Sex Hormones

Look at Fig. 7.3 again. The hormones

secreted by the pituitary stimulate testes

Fig. 7.5 : Position of endocrine glands in the

human body

pituitary

gland

thyroid gland

adrenal

gland

pancreas

testis

position of

the ovary in

the female

Boojho and Paheli had once visited

their aunt who was a doctor and

remembered that a boy named Kaka had

a very big and bulging throat. Their aunt

had told them that Kaka was suffering

from ‘goitre’, a disease of the thyroid

gland. Kaka’s thyroid gland was not

producing the hormone thyroxine.

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Their aunt also told them that their

uncle was suffering from ‘diabetes’

because his pancreas was not producing

the hormone insulin in sufficient

quantities. Boojho and Paheli then

asked their aunt about the adrenal

glands, which are also shown in the

chart hung on the wall of her clinic. The

aunt told them that adrenal glands

secrete hormones which maintain the

correct salt balance in the blood.

Adrenals also produce the hormone

adrenalin. It helps the body to adjust

to stress when one is very angry,

embarrassed or worried.

Thyroid and adrenals secrete their

hormones when they receive orders from

the pituitary through its hormones.

Pituitary also secretes growth hormone

which is necessary for the normal

growth of a person.

controlled by insect hormones. In a

frog, it is controlled by thyroxine, the

hormone produced by thyroid.

Thyroxine production requires the

presence of iodine in water. If the water

in which the tadpoles are growing does

not contain sufficient iodine, the

tadpoles cannot become adults.

7.8 Role of Hormones in

Completing the Life

History of Insects and

Frogs

You have already learnt about the life

cycle of the frog. The tadpole passes

through certain stages to become a frog

(Chapter 6). This change from larva to

adult is called metamorphosis

(Fig. 6.10). Metamorphosis in insects is

Collect information from magazines

or from doctors and prepare a note

on the importance of consuming

iodised salt. You can also look for

this information on the internet.

7.9 Reproductive Health

The physical and mental well being of

an individual is regarded as an

individual’s health. To keep the body

healthy, every human being, at any age,

needs to have a balanced diet. The

person must also observe personal

hygiene and undertake adequate

physical exercise.

During adolescence, however, these

become even more essential as the body

is growing.

Nutritional Needs of the Adolescents

Adolescence is a stage of rapid growth

and development. Hence the diet for an

Are there hormones in

other animals also? Have

they any role to play in

reproduction?

If people do not have

enough iodine in their diet,

will they get goitre caused

by lack of thyroxine?

Activity 7.3

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REACHING THE AGE OF ADOLESCENCE

adolescent has to be carefully planned.

You have already learnt what a balanced

diet is. Recall that a balanced diet means

that the meals include proteins,

carbohydrates, fats and vitamins in

requisite proportions. Our Indian meal

of roti/rice, dal (pulses) and vegetables

is a balanced meal. Milk is a balanced

food in itself. Fruits also provide

nourishment. For infants, mother’s milk

provides all the nourishment that

they need.

Iron builds blood and iron-rich food

such as leafy vegetables, jaggery, meat,

citrus, Indian gooseberry (amla) are good

for adolescents.

Check items for lunch and dinner in

your meal. Is the meal balanced and

nutritious? Does it include cereals

which give energy and milk, meat, nuts

and pulses which provide proteins for

growth? Also, does it include fats and

sugar that give energy? What about

fruits and vegetables which are

protective foods? Chips and packed or

tinned snacks, though very tasty

should never replace regular meals as

they do not have adequate nutritional

value.

Activity 7.4

Make a group with your friends.

Write down the items of food in your

breakfast, lunch and dinner you

had on the previous day. Identify

the items responsible for proper

growth. Also identified the junk

food that you consumed the

previous day.

Personal Hygiene

Everyone should have a bath at least

once everyday. It is more necessary for

teenagers because the increased activity

of sweat glands sometimes makes the

body smelly. All parts of the body should

be washed and cleaned everyday. If

meat

vegetables

fruits

milk and

eggs

grains

Fig. 7.6 : Nutritious items of food

Activity 7.5

Get ideas from the pictures given in

Fig.7.6. Prepare charts or posters

and paste them in the class so that

you are aware of the diet for

adolescents. You may use your

creative ideas and present it like an

advertisement. You may even

organise a competition on this topic.

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SCIENCE88

cleanliness is not maintained there are

chances of catching bacterial infection.

Girls should take special care of

cleanliness during the time of menstrual

flow. They should keep track of their

menstrual cycle and be prepared for the

onset of menstruation. Use sanitary

napkin or clean homemade pads.

Change pads after every 4–5 hours as

per the requirement.

Physical exercise

Walking and playing in fresh air keeps

the body fit and healthy. All young boys

and girls should take walks, exercise

and play outdoor games.

Activity 7.6

Collect data on the number of

children in your class who exercise

regularly and who do not exercise

regularly. Did you notice any

difference in their fitness and

health? Prepare a report on the

benefits of regular exercise.

Say “NO” to Drugs

Adolescence is a period of much

activity in the body and mind which

is a normal part of growing up. So do

not feel confused or insecure. If

anybody suggests that you will get

relief if you take some drugs, just say

‘No’ unless prescribed by the doctor.

Drugs are addictive. If you take them

once, you feel like taking them again

and again. They harm the body in the

long run. They ruin health and

happiness.

You must have heard about AIDS

which is caused by a dangerous virus,

HIV. This virus can pass on to a

normal person from an infected

person by sharing the syringes used

for injecting drugs. It can also be

transmitted to an infant from the

infected mother through her milk. The

virus

can also be transmitted through

sexual contact with a person infected

with HIV.

Adolescent Pregnancy

You might be knowing that in our country, the legal age for marriage is 18 years

for girls and 21 years for boys. This is because teenage mothers are not prepared

mentally or physically for motherhood. Early marriage and motherhood cause health

problems in the mother and the child. It also curtails employment opportunities for

the young woman and may cause mental agony as she is not ready for

responsibilities of motherhood.

Myths, Taboos, Do’s and Don’ts

You have learnt here and from Chapter

6 the scientific facts related to human

reproduction. There are many wrong

notions which you should now be able

to discard as informed adolescents. For

example, there are myths and taboos

regarding bodily changes that

adolescents experience. Some of these

are given below and you can now argue

why these are myths and not facts.

1. A girl becomes pregnant if

she looks at boys during

menstruation.

2. The mother is responsible for the

sex of her child.

3. A girl should not be allowed to

work in the kitchen during

menstruation.

You may come across many other myths

and taboos. Discard them.

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REACHING THE AGE OF ADOLESCENCE

KEYWORDS KEYWORDS

KEYWORDS

ADAM’S APPLE

ADOLESCENCE

ADRENALIN

BALANCED DIET

ENDOCRINE GLANDS

ESTROGEN

HORMONES

INSULIN

LARYNX

PITUITARY GLAND

PUBERTY

REPRODUCTIVE

HEALTH

SECONDARY SEXUAL

CHARACTERS

SEX CHROMOSOMES

TARGET SITE

TESTOSTERONE

THYROXINE

VOICE BOX

WHAT YOU HAVE LEARNT WHAT YOU HAVE LEARNT

WHAT YOU HAVE LEARNT

Ü Humans become capable of reproduction

after puberty sets in. Children between the

ages of 11 and 19 years are called adolescents.

Ü The onset of puberty brings about growth of

the reproductive organs. Hair grow at

various places on the body. Breasts develop

in girls and facial hair (moustache and beard)

appear in boys. Voice of boys becomes hoarse

as voice box enlarges during adolescence.

Ü Children gain height during adolescence.

Ü The onset of puberty and maturity of

reproductive parts are controlled by hormones.

Ü Hormones are secretions of endocrine glands

which pour them directly into the blood stream.

Ü Pituitary gland secretes hormones which

include growth hormone and hormones that

make other glands such as the testes, ovaries,

thyroids and adrenals, secrete hormones.

Pancreas secretes insulin, thyroid produces

thyroxine and adrenals produce adrenalin.

Ü Testosterone is the male hormone and

estrogen, the female hormone. The uterine wall

in females prepares itself to receive the

developing fertilised egg. In case there is no

fertilisation, the thickened lining of the uterine

wall breaks down and goes out of the body

along with blood. This is called menstruation.

Ü Sex of the unborn child depends on whether

the zygote has XX or XY chromosomes.

Ü It is important to eat balanced food and

maintain personal hygiene during

adolescence.

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Exercises

1. What is the term used for chemical secretions of endocrine glands

responsible for changes taking place in the body?

2. Define adolescence.

3. What is menstruation? Explain.

4. List changes in the body that take place at puberty.

5. Prepare a Table having two columns depicting names of endocrine glands

and hormones secreted by them.

6. What are sex hormones? Why are they named so? State their function.

7. Choose the correct option.

(a) Adolescents should be careful about what they eat, because

(i) proper diet develops their brains.

(ii) proper diet is needed for the rapid growth taking place in their

body.

(iii) adolescents feel hungry all the time.

(iv) taste buds are well developed in teenagers.

(b) Reproductive age in women starts when their

(i) menstruation starts.

(ii) breasts start developing.

(iii) body weight increases.

(iv) height increases.

(i) chips, noodles, coke.

(ii) chapati, dal, vegetables.

(iii) rice, noodles and burger.

(iv) vegetable cutlets, chips and lemon drink.

8. Write notes on—

(a) Adam’s apple.

(b) Secondary sexual characters.

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REACHING THE AGE OF ADOLESCENCE

9. Word game : Use the clues to work out the words.

Across

3. Protruding voice box in boys

4. Glands without ducts

7. Endocrine gland attached to brain

8. Secretion of endocrine glands

9. Pancreatic hormone

10. Female hormone

Down

1. Male hormone

2. Secretes thyroxine

3. Another term for teenage

5. Hormone reaches here through blood stream

6. Voice box

7. Term for changes at adolescence

E X E R C I S E S

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10. The table below shows the data on likely heights of boys and girls as they

grow in age. Draw graphs showing height and age for both boys and

girls on the same graph paper. What conclusions can be drawn from

these graphs?

Height (cm)

Boys Girls

0 53

4 96

8 114 110

12 129 133

16 150 150

20 173 165

Age

(Years)

Extended Learning — Activities and Projects

1. Find out from your elder relatives about their awareness of the

legal status of early marriage. You yourself may get information on

it from your teacher, parents, a doctor or the internet. Write a two-

minute speech explaining why early marriage is not good for the

couple.

2. Collect newspaper cuttings and information in magazines about HIV/

AIDS. Write a one page article of 15 to 20 sentences on HIV/AIDS.

3. In our country, according to 2011 census, there are 940 adolescent

females for every 1000 males. Find out.

(a) the concerns of the community regarding this low ratio.

Remember that the chance of having a boy or a girl is equal.

(b) what amniocentesis is and how useful this technique is. Why

is its use for identification of sex of the unborn child banned

in India?

4. Put your ideas together and write a short note on the importance of

knowing facts about reproduction.

For more information visit :

l www.teenshealth.org/teen/sexual_health/

l www.adolescenthealth.com

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